If you are asking where more people go to search homes, I believe the figures would unanimously show Realtor.com. I have bought several tools to market properties and our brand on Realtor.com for office and they have worked very well for us.
If you are talking about where most agents buy websites, I am not sure. I used to use Point2. Good site for $50 a month. I recently switched, after much research I might add, to A La Mode. i went there because i bought a package that would allow me to provide sites to all of my agents for FREE. Free to the agents that is. Completely customizable content and unlimited pages, lead generation tools, etc...
Good luck and feel free to call me to ask more questions about either of these providers.
Agents, if that is what you are looking for... And do you mean searches conducted by the buying public?
Edith YourRealtor4Life & Chicago Connection
Working always in the best interest of her clients